Process for oxidizing quinodimethanes to form aromatic carboxylic acids



United States Patent 1965, Ser. No. 4%,292

4 Claims. (Cl. 260-524) This application is a division of my prior andcopending application Serial No. 221,375, filed September 4, 1962.

This invention relates to new improvements in the chemistry ofquinodimethane (xylylenes).

It is known that p-xylene and related compounds may be pyrolyzed so asto prepare polymers. It is also known that pyrolysis of p-xylene andrelated compounds may be carried out in a manner so as to quench thepyrolyzate prior to the preparation of a polymer. In this manner,monomeric quinodimethanes are prepared in solution form. The solutionmay then be utilized to react by various mechanisms so as to form avariety of polymers and compounds.

It is an object of this invention to expand upon the technology relatingto the pyrolysis of p-xylene and related compounds, especially as itpertains to preparation and use of quinodimethanes.

Another object is to teach various techniques for increasing the yieldof quinodimethanes during pyrolysis.

Another object is to teach reacting a quinodimethane with N0 Anotherobject is to teach the gas phase synthesis of an organic compound byreacting dissimiliar free radical sources. Various other objects andadvantages of the present invention will become apparent to thoseskilled in the art from the accompanying description and disclosure.

The term quinodimethane as used herein means an organic compound havinga diunsaturated six-membered cyclic nucleus having each of two carbonatoms of the diunsaturated ring doubly bonded to the carbon atom of amethylene group. The methylene group may be substituted orunsubstituted. The diunsaturated ring which is common to each of thequinodimethanes will be positioned according to whether the methylenegroups are ortho or para to each other. The preferred quinodimethanes ofthis invention are those having a symetrically diunsaturatedsix-membered ring to which a methylene group is doubly bonded topara-positioned carbon atoms of the ring. The term quinodimethane asused herein includes those compounds which contain only the one ringsuch as, for example, in p-quinodimethane (also called p-xylylene) whichhas the structure:

as well as those compounds in which the quinoid ring is fused to one ormore aromatically unsaturated sixmembered rings such as, for example, in1,4-naphtha quinodimethane which has the structure:

"ice

The aromatically unsaturated ring which is fused to the ring is referredto herein as the benzenoid ring.

It is to be understood that the quinodimethane starting material of thisinvention may be a carbocyclic compound, i.e. a cyclic compound in whicheach atom of the cyclic skeleton is a carbon atom such as inp-quinodimethane and 1,4-naphthaquinodimethane; or it may be anitrogen-containing heterocyclic compound, i.e. a compound having atleast one nitrogen atom as part of the cyclic skeleton. The heterocycliccompounds are preferably those in which the nitrogen is vicinal only tocarbon and include those in which nitrogen is a constituent of thequinoid ring or the benzenoid ring.

The groups which are singly bonded to the cyclic skeleton of thequinodimethane are referred to herein as the nuclear substituents andmay be hydrogen, halogen, alkyl, aryl, alkoxy, or aryloxy radicals.These substituents of the dicyclic compounds may be the same ordifferent, and may be on the quinoid ring or on the benzenoid ring or onboth rings. The methylene groups which are doubly bonded to thequinodimethane ring may be unsubstituted methylene groups, i.e. (CH orthey may be substituted with halogen, alkyl, aryl, aralkyl, alkoxy, andaryloxy groups without departing from the scope of this invention.

The preferred quinodimethanes are those of the group consisting ofp-quinodimethane, 1,4-naphthaquinodimethane, and correspondingheterocyclic quinodimethanes containing at least one heteronitrogen atomvicinal only to carbon atoms and the nuclear substitution products ofthe foregoing members with atoms of the normally gaseous halogens andmethyl groups.

Among the specific carbocyclic aromatic compounds which can be pyrolyzedto produce the aforesaid quinodimethanes which are used as a reactant inaccordance with the process of this invention are: p-xylene;pseudocumene; durene; isodurene; prehnitene; pentamethyl benzene;hexamethyl benzene; 1,4-dimethyl naphthalene; 1,2,3,4,6,7 hexamethylnaphthalene; 2-chloro-p-xylene; 2 fluoro-p-xylene; 2,5 difluoro-xylene;2,5 dichloro-pxylene; 2,3,5-trichloro-p-xylene; 2,3,5trifluoro-p-xylene; 2,3,5,6 tetrachloro p xylene;2,3,5,6-tetrafluoro-p-xylene; 2-chloro-3,5,6-trimethyl benzene;6-chlor0-l4,-dimethyl naphthalene; and 2,3,6,7-tetrachloro-1,4-dimethylnaphthalene. Among the specific aromatically unsaturatednitrogen-containing heterocyclic compounds which are pyrolyzed to yieldthe heterocyclic quinodimethanes which are reacted as described hereinare: 2,5-dimethyl pyrazine; 2,5-lutidine; 2,5-dimethyl pyrimidine;5,8-dimethyl quinoline; 1,4-dimethyl isoquinoline; 5,8-dimethylisoquinoline; 5,8-dimethyl quinazoline; 5,8-dimethyl quinoxaline;2,3,5-trirnethyl pyrazine; 2,3,5,6-tetramethyl pyrazine; 2,3,5-trimethylpyridine; 2,4,5-trimethyl pyridine; 5,6,8-trimethyl quinoline; and2,5-dimethyl-6-chloropyrazine.

The pyrolysis of the aforesaid 1,4-dimethyl substituted aromaticcompounds is preferably carried out at a temperature within the range ofabout 900 C. to about 1300 C., for example, at about 1000 C. For bestresults the aromatic vapor should be present at a partial pressure ofless than mm. mercury. The N0 can be prepared by pyrolysis of nitricacid or supplied from a separate source as illustrated below. Thepyrolysis can be conducted in the presence of an inert gas, such ascarbon dioxide, steam or nitrogen, particularly when the partialpressure of the aromatic compound is 10 mm. mercury or below. Within thepreferred pyrolysis temperature range the contact time should be withinthe range of from about 0.1 to about 0.001 second. In those cases wherethe quinodimethane is the desired product, the pyrolyzed vapors arequenched in a liquid maintained at a temperature below 45 C.

The liquid used for quenching and storing of the quinodimethane may beof any composition which remains liquid at the necessary temperaturerange and which has a relatively low partial pressure at about 45 C.consistent with the upper total pressure limit of 400 mm. mercurypressure and preferably low enough to permit operation below 10 mm.mercury pressure. The liquid also should be substantially non-reactivewith the quinodimethane formed, although liquids which react to someslight degree may be used. Among the specific liquids which may be usedfor quenching are the parafiinic and cycloparafiinic hydrocarbons of lowfreezing point, such as hexane, petroleum ether, cyclopentane and1,4-dimethyl cyclohexane; the aromatic hydrocarbons of low freezingpoint, such as toluene, ethyl benzene, o-ethyl toluene and m-diethylbenzene; the halogenated hydrocarbons of low freezing point, such aso-chlonoethyl benzene, o-finoro toluene and 1,1-dichloroethane; carbonylcompounds of low freezing point such as acetone, methyl ethyl ketone andmethyl isobutyl ketone; ethers of low freezing point, such as diethylether, ethyl n-propyl ether and tetrahydrofurane; alcohols of lowfreezing point, such as methanol, ethanol and isopropyl alcohol; andother normally liquid compounds of low freezing point, such as carbondisulfide. If desired, liquids of low freezing point may be obtained bythe blending of two or more compounds of higher freezing point. Forexample, mixtures of carbon tetrachloride and chloroform may be used.

EXAMPLE This example illustrates the results obtained by the pyrolysisof p-xylene and nitric acid under varying conditions.

A. Co-pyrolysis of p-xylene and HNO to produce nitrogen free compoundsThe pyrolysis system shown in L. A. Errede and B. F. Landrum, J. Am.Chem. Soc., 79, 4952 (1957), was modified to include a second vaporizerfor metering aqueous HNO (68%). The system was evacuated to 6 mm. Hgpressure and p-xylene (3.27 moles) and HNO (1.05 moles) were metered tothe system at the rate of 0.045 and 0.015 mole/min, respectively. Thetwo gas streams were mixed before they entered the furnace where fastflow pyrolysis occurred at 1030 C. The pyrolyzate was collected in 4liters of hexane kept at -78 C. The cold trap was warmed to roomtemperature to afford a threephase mixture of hexane solution, aqueousacid solution (43 g.) and a black tar (9 g.). Large volumes of N weregiven off when the mixture was warmed to room temperature. The lasttraces were removed by a current of nitrogen. The hexane solution waswashed with water and the solvent was removed by rapid evaporation at100 C and mm. Hg pressure. The yellow liquid residue (154 g.) was amixture of aldehydes and aromatic hydrocarbons having no NO groups asindicated by infrared analysis and a negative qualitative test for N0using ferrous ammonium sulfate in alcoholic potassium hydroxide. Themixture was separated by distillation at atmospheric pressure to give 3main fractions. (1) 76 g., B.P. 137-141 C. This was identified byinfrared analysis as p-xylene; (2) 32 g., B.P. l96-202 n =l.5433. Thiswas identified as p-tolualdehyde by infrared analysis and by convertinga sample to its 2,4-dinitrophenylhydrazone derivative (M.P. 229230 C.,no depression with known sample); (3) 35 g. residue. The residue wasseparated further by distillation at 2 mm. Hg pressure to give 3additional major fractions. (1) 2.2 g., B.P.

67-80 C. Infrared analysis indicated that this was .4 mostlyp-tolualdehyde with some 1,4-dip-tolylethane and diarylrnethanes presentas impurities; (2) 18.7 g., B.P. 125-137 C. Infrared analysis indicatedthat this was a mixture of 1,4-di-p-tolylethane, diarylmethanes and asmall amount of acid material. The mixture was extracted with dilutesodium hydroxide and the residue was dissolved in methanol. The methanolsolution was chilled to 78 C. to precipitate di-p-tolylethane (4.5 g.)in the form of pearl white platelets (M.P. 74-75 C., no depression withknown sample). The methanol solution was evaporated to dryness leaving aresidue (10 g.) which was a mixture of alkylated diphenylmethanes and1,4-dip-tolylethane as indicated by infrared analysis; (3) 9 g. residue,B.P. 150 C. Infrared analysis indicated that this was a complex mixtureof aromatic hydrocarbons and some acidic material. The residue wasleached with dilute sodium hydroxide. The alkaline extract was combinedwith corresponding extract from Fraction 2 and the resulting solutionwas acidified with hydrochloric acid to liberate the organic acid (3 g.)which was removed by filtration. The acid was recrystallized from hotwater to yield p-toluic acid in the form of fine white needles (M.P.l74-175 C., no depression with known sample). The compound was alsoidentified by its infrared spectrum.

Thus, 3.2 moles of p-xylene and 1.05 moles of .HNO were co-pyrolyzed toalford 0.28 moles of p-tolualdehyde, 0.02 moles of p-toluic acid, and0.24 moles of p-methylbenzyl radical equivalents isolated as itsdaughter products, 1,4-di-p-tolylethane and diarylethane.

B. Reaction of pyrolyzed p-xylene with non-pyrolyzed HNO to producenitrogen containing compounds p-Xylene (1.8 moles) was metered at therate of 0.025 mole/min, to the pyrolysis system evacuated to 2 mm. Hg.Pyrolysis occurred at 1030 C. for an average residence time of 0.006sec. These conditions are known to produce about 0.2 mole ofp-methylbenzyl radicals. At a point 6.5 inches downstream from thepyrolysis zone, the pyrolyzate was mixed with non-pyrolyzed HNO (10moles), metered counter-current to the system at the rate of 0.142mole/min. The temperature at the blend point was about 450 C. The gasmixture was collected about 3 feet from the blend point in hexane (4liters) kept at 78 C. The absence of NO and N0 in the liquid nitrogenand Dry Ice traps, respectively, indicated that little or no thermaldegradation of HNO had occurred.

The resulting pyrolyzate solution was warmed to room temperature. About1 g. of poly-(p-xylylene was isolated as film that adhered to the wallsof the receiver about the level of the liquid. The acid aqueous andorganic phases were separated by means of a separatory funnel.

The organic layer was extracted with dilute aqueous NaOH, but no organicacid was liberated when the alkaline solution was acidified with HCl.The hexane in the organic phase was removed by distillation atatmospheric pressure. The residue (26 g.) was separated by distillationat 8 mm. Hg pressure to give two fractions. (1) 11 g., B.P. 103-104 C.The infrared spectrum was similar to that of nitro-p-xylene. The indexof refraction (n =1.536) and density (n =l.l49) of the light yellow oilwas in agreement with the correspond ing data measured on known sample(n "==1.539; d: 1.148). A small sample of this oil (1.5 g.) was oxidizedby K Cr O (11 g.) in H 80 and H 0 to 3-nitro-p-toluic acid (M.P. 186-187C.). (No depression with known sample.) (2) 15 g. residue. The infraredspectrum indicated that this was a mixture of nitro-aromatic compounds.

The aqueous HNO plane was diluted with water and a copious precipitateformed immediately. The product g.) was a mixture of nitroxylenes asindicated by infrared analysis. Repeated fractional crystallization fromtoluene and methanol gave three major fractions classified according tomelting point. (1) 2.4 g., M.P.

9798 C., the elementary analysis (49.3% C, 4.7% H, 13.4% N) correspondedto the empirical (formula for dinitroxylene, C H N O (C, 49.0; H, 4.1).The infrared spectrum, however, indicated that this was a mixture ofnitroxylenes, probably the 2,3 and the 2,6-di-nitroqpxylylene sincethese are known to form a one to one adduct that melts at 99 C. (2) 40g., M.P. 95-102 C.; infrared spectrum was similar to Fraction 1 andindicated a mixture of nitro-xylenes. (3) 51 g., M.P. 7988 C. This toowas a mixture of nitro-xylenes as indicated by infrared analysis.Fractions 2 and 3 and the nitroxylenes residue from the organic layerwere reconstituted and an attempt was made to separate the product byliquid chromatography. The results were no better than those realizedvia fractional recrystallization. A small sample (1 g.) M.P. 92-93 C.was isolated, however, which could be 2,3-di-nitro-p-xylene (lit. 93 C.)

In summary, 1.8 moles of p-xylene were pyrolyzed and the pyrolyzate wasquenched with 10 moles of nonpyrolyzed HNO to give about 0.55 mole ofdi-nitro-pxylene (30% yield) and about 0.07 mole of nitro-pxylene (4%yield). No organic acid or aldehydes were isolated despite the formationof about 0.2 mole of p-methylbenzyl radicals before quenching with HNOC. Co-axial pyrolysis of p-xylylene and HNO The internal thermowell ofthe pyrolysis system used in A above was replaced by an open end quartztube through which HNO could be metered to the pyrolysis system. Thistube extended to a point 3 inches beyond the furnace so that blending ofthe pyrolyzed nitric acid stream and the pyrolyzed p-xylene stream wouldoccur at a point 6.5 inches away from the pyrolysis zone. The space inthe outer concentric tube between the pyrolysis zone and the blend pointwas filled with five quartz tubes (6" long, 6 mm. D,, 4 mm. ID.) toensure complete conversion of p-methylbenzyl radicals to p-xylylene inthe p-xylene pyrolyzate before the hydrocarbon stream reached the blendpoint. The temperature was recorded by means of a sliding thermocoupleplaced between the furnace and the outer pyrolysis tube. The system wasevacuated to 4 mm. Para-xylene (1.98 moles) and HNO (3.4 moles) weremetered separately to the system through the concentric tubes at therate of 0.016 and 0.027 moles/min, respectively. Pyrolysis of pxyleneoccurred at 930 C. for 0.01 sec. (conditions which are known to giveabout 0.24 mole of p-methylbenzyl radicals). The pyrolyzate mixture wascollected in hexane (4 liters) kept at 78 C. The resulting mixture waswarmed to room temperature with evolution of N0 The last traces of N0were removed by a stream of nitrogen. A three-phase system was obtainedand this was separated into its aqueous liquid and organic solidcomponents. The solid (27 g.) was dissolved in aqueous Na CO The organicphase was extracted with aqueous Na CO The two alkali carbonatesolutions were combined and then acidified with aqueous HCl. The organicacid liberated (26 g.,0.16 mole) was collected by filtration. The acidwas leached with methanol but none dissolved indicating the absence ofp-toluic acid. The acid did not melt below 300 C. Its infrared spectrumwas substantially identical with that of terephthalic acid. A smallsample was converted to its dimethyl ester by treatment with fused PCland subsequent addition to methanol. The melting point of the dimethylterephthalate (M.P. 138-139' C.) produced in this way showed nodepression when mixed with a known sample. The hexane solution wasevaporated to dryness and a mixture of aromatic hydrocarbons wasobtained as residue (9 g.).

Thus, pyrolysis of p-xylene (1.98 moles) was carried out in such a wayas to afford about 0.24 mole of. pmethylbenzyl radicals and about 70% ofthese were iso lated as terephthalic acid and about 30% as a mixture ofaromatic hydrocarbons (1,2-di-p-t-oly1ethane, methylated diphenylmethanes and anthracenes).

D. Pyrolyzed p-xylene collected in the presence of HNO to producenitrogen containing compounds p-Xylene (1.88 moles) was pyrolyzed at1000 C. and 4 mm. for 0.008 sec. residence time. The pyrolyzate wascollected in a slurry of solid HNO (8.5 moles) in toluene (4 liters)kept at 78 C. The reaction mixture was warmed to room temperature andseparated. No organic acid was isolated. 22% of the p-xylene metered tothe system was isolated as nitro-p-xylene, 2% as di-nitro-pxylene, 6% asnitrated poly-(p-xylylene) containing 7.4% N and 1% as p-methylbenzylnitrate (B.P. -111 C. .at 10 mm., rz =1.5174, d =1.153).

Calc. for C H NO C, 57.49; H, 5.42; MR 43.57. Found: C, 57.7; H, 5.35;MR 43.7.

A sample of p-methylbenzyl nitrate was prepared by reaction ofpulverized AgNO with p-methylbenzyl chloride in ether. The physicalconstants and the infrared spectra of this sample were substantially thesame as those given above.

E. Co-axial pyrolysis of p-xylene and N0 to produce nitrogen freecompounds The pyrolysis system of C above was evacuated to 5 mm.p-xylene (7.3 moles through the outer tube) and N0 (25.6 moles throughthe inner tube) were metered to the system at the rate of 0.0545 and0.175 mole/min, respectively. Pyrolysis of p-xylene occurred at 1000 C.for 0.002 sec. and the two pyrolyzate streams were allowed to blend at apoint 6.5 inches away from the end of the mutual pyrolysis zone.Previous experiments had shown that the pyrolysis conditions used inthis experiment afford about 0.18 mole of p-methylbenzyl radicals andthat about 40% of these are converted to p-xylylene by the time the.hydrocarbon stream reaches the blend point where the temperature isabout 450 C. The pyrolyzate mixture was collected in hexane kept at 78C. When the resulting solution was warmed to room temperature, the usualthree phase mixture was obtained. The solid (9 g.) was removed byfiltration, dissolved in aqueous Na CO and reprecipitated by addition ofHCl. This product was identified as terephthalic acid by its infraredspectrum. The organic layer was extracted with aqueous Na COAcidification of the extract with dilute HCl gave 11 g. of impurep-toluic acid (170 C.). The organic layer was evaporated to dryness anda mixture of aromatic hydrocarbons (1,2-di-p-tolyleth-ane anddiarylmethanes) was obtained as residue (6 g.).

I claim:

1. A method for the preparation of aromatic carboxylic acid comprisingthe steps of:

(a) pyrolyzing a gas stream comprising p-xylene,

(b) pyrolyzing a gas stream comprising a material selected from thegroup consisting or HNO and N0 (c) blending the respective resultingstreams of pyrolyzates at temperatures below the pyrolysis temperatures,and

(d) recovering aromatic carboxylic acid from the reaction products ofthe combined pyrolyzate streams.

2. In a method for the preparation of terephthalic acid from p-xylylene,the improvement which comprises contacting under vapor phase conditionsat an elevated temperature p-xylylene with a previously pyrolyzedmaterial selected from the group consisting of HNO and N0 3. A methodfor the preparation of terephthalic acid comprising the steps of:

(a) pyrolyzing p-xylene under conditions such that p-xylylene isproduced,

(b) pyrolyzing a material selected from the group consisting of HNO andN0 (0) blending the pyrolyzates at temperatures below the pyrolysistemperature, and

(d) recovering terephthalic acid from the products of the blendedpyrolyzates.

4. The method of claim 3 wherein the blended py- FOREIGN PATENTSrolyzates are quenched in a non-reactive liquid having a relatively lowpartial pressure at a temperature of about 662,139 12/1951 Great Britaim823,437 11/1959 Great Britain.

References Cited by the Examiner UNITED STATES PATENTS 1,694,122 12/1928Iaeger 260-524 5 LORRAINE A. WEINBERGER, Primary Examiner.

S. B. WILLIAMS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3,299,126 January 17, 1967 Louis A. Errede It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 2, line 43, for "14" read 1,4 column 3, line 47, for "3.27"read-- 3.17 column 4, line 70, for "plane" read phase Signed and sealedthis 21st day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents At-testing Officer UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3, 299,126 January 17, 1967 LouisA. Errede It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

for "14" read 1,4 column 3, line Column 2, line 43,

-; column 4, line 70, for "plane" 47, for "3.27" read 3.17 read phaseSigned and sealed this 21st day of November 1967 (SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A METHOD FOR THE PREPARATION OF AROMATIC CARBOXYLIC ACID COMPRISINGTHE STEPS OF: (A) PYROLYZING A GAS STREAM COMPRISING P-XYLENE, (B)PYROLYZING A GAS STREAM COMPRISING A MATERIAL SELECTED FROM THE GROUPCONSISTING OR HNO3 AND NO2, (C) BLENDING THE RESPECTIVE RESULTINGSTREAMS OF PYROLYZATES AT TEMPERATURES BELOW THE PYROLYSIS TEMPERATURES,AND (D) RECOVERING AROMATIC CARBOXYLIC ACID FROM THE REACTION PRODUCTSOF THE COMBINED PYROLYZATE STREAMS.